A drafting head of this type is, for example, known from German Reference in which disposed laterally on the gripping member are two actuating elements, namely pushbuttons, and upon actuation are displaceable approximately parallel to the drawing plane for setting the different switching statuses of the drafting head. With the first actuating element, the normal side of the drafting head can be disengaged and can free-switch over into an over stroke position. With the other actuating element, the normal side of the drafting head can be firmly locked in the actual position. In the case of known type drafting heads, the actuating elements are arranged such that they can be actuated by the tips of the fingers of a user hand resting on the gripping member. Usually, the actuating elements are actuated with the thumb, while the other fingers are used for firmly holding the gripping member and for rotating the drafting head. After disengaging or free-switching the normal side of the drafting head, often occurring during use is that the drafting head is rotated by the user hand that is resting on the gripping member, and firmly holding onto this latter, into a position in which the thumb and also the other fingers no longer find themselves within reach of the second actuating element for locking the normal side of the drafting head. Now, in order that the actuating element for locking be capable of being actuated by the fingers, preferably the thumb, of the hand of the user resting on the gripping member, their position relative to the gripping member must be changed, which is possible only by pivoting or rotating the hand of the user relative to the gripping member, or even by completely letting go of the gripping member and shifting the user's hand. This leads not only to a troublesome manipulation of the drafting head when locking but also frequently to the drafting head being displaced out of the previously-attained working position by the movement of the user's hand. It is indeed also conceivable, in place of the hand resting on the gripping member, to use the other hand for actuation of the actuating element for locking; however, this method of proceeding is likewise really troublesome, since usually the other hand is holding the drafting stylus which, before operating the actuating element for locking, must then first be laid aside.
Therefore, the object of the invention is to further develop a drafting head of the initially-mentioned type such that for locking used will be the user hand that is resting on the gripping member, without its position relative to the gripping member needing to be changed.
This objective, in the case of the drafting head of the initially mentioned type, is satisfied in accordance with the invention by the fact that the actuating element for locking is arranged on the gripping member such that it lies against the inner surface of the ball of the thumb of the user hand resting on the gripping member. Preferably, the actuating element for disengaging and/or free-switching is disposed within the gripping range of the user hand resting on the gripping member.
The advantage of the invention lies particularly in the fact that the drafting head can be switched by the user hand resting on the gripping member into a disengaging of free-switching status, and maintained in this condition, while the actuating element for locking can simultaneously be actuated with the ball of the thumb of the user hand resting on the gripping member and, in this manner, the drafting head can be locked in the actual position set after releasing, without the position of the user hand relative to the gripping member having to be changed, or even having to use the other hand. This is achieved in accordance with the invention by the fact that the actuating element for locking continually--therefore also when rotating the drafting head--rests against the inner surface of the ball of the thumb of the user hand resting on the gripping member. Disengaging and/or free-switching, as well as locking of the normal side of the drafting head can, therefore, be executed only by the hand of the user that is resting on the gripping member, thereby, for locking, the hand of the user does not need to be pivoted relative to the gripping member nor removed therefrom.
Preferably, the actuating element for disengaging and/or free-switching is coupled with the actuating element for locking in such manner that when free-switching the normal side of the drafting head a previously-set locking is released.
According to a particularly preferred form of embodiment of the invention, the actuating element for locking is disposed on the gripping member such that its actuation can be accomplished by means of an actuating force acting perpendicularly to the drawing plane, and in so doing, the actuating element can move toward the drawing plane. This form of embodiment of the invention has the advantage that when actuating the actuating element for locking, no force components that could displace the drawing head are active parallel to the drawing plane. By applying the actuating force perpendicularly to the drawing plane, the drafting head remains in the previously set working position.
The actuating element for locking is preferably constructed as a pivot lever that is pivotable about a pivoting axis running parallel to the drawing plane. In order to realize an ergonimically-favorable maneuverability, this actuating element has at the free end of the pivot lever a thickened section that is partially drawn over the bulge of the gripping member and that rests in large-surface fashion against the inner surface of the user hand resting on the gripping member.
Another preferred form of embodiment of the invention is characterized by the fact that, for disengaging and/or free-switching the normal side of the drafting head, there are disposed opposite to one another a first and a second actuating element, and displaying an opposingly-aligned actuating path, and that a first switching status can be set only with simultaneous actuation of both actuating elements. The advantages of this design lie particularly in the fact that there are provided on the gripping member two actuating elements with a counter-running path of movement and that for setting a first switching status both actuating elements are actuated simultaneously--and oppositely to one another--so that the actuating forces acting opposingly on the drafting head are removed. A displacement of the drafting head is reliably prevented in this manner.
In order to be able to set still other switching statuses with the first and the second actuating element, preferably produced is a second switching status by actuation of the first and/or of the second actuating element.
Particularly preferred, one of the switching statuses can also be adjusted by setting the first and second actuating element commonly into an over stroke position, so that this switching status can also be set without the one-sided reaction of the actuating forces.
Preferably, in the first switching status, the normal side of the drafting head is freely switched, so that the normal side is freely rotatable without engaging into the notch positions. This first switching status is set by simultaneous actuation of the first and of the second switching elements. As a second switching status, by actuating the first or the second actuating element, the normal side of the drafting head can be released from a notched position.
The first and the second actuating elements are preferably constructed as rocker keys that pivot over a small pivoting angle about pivot pins that are attached to the gripping member at a predetermined distance from the base plate.
All actuating elements are preferably biased in their at-rest position by means of springs, so that after actuation they can again assume their initial position.
According to a particularly preferred form of embodiment of the invention, the gripping member is constructed as an oblong bulge whose height perpendicularly relative to the drawing plane is greater than its width parallel to the drawing plane. The bulge-shaped gripping member preferably has, transversely to its longitudinal direction, a cross section having approximately the form of a U- or V-profile, with the base of the U- or V-profile being directed upwardly and capable of being gripped about by the palm of the user's hand. In the longitudinal direction of the oblong bulge, the gripping member has approximately the form of a segment of a circular disk. The upwardly-pointing contour of the bulge, in its longitudinal direction, is approximately circularly curved up to the base plate of the drafting head.
Advantageous further developments of the invention are characterized by the features of the subclaims.